建平县农业生态系统结构总体设计的研究

农业生态系统结构的总体设计是农业生产发展的客观要求,同时,也是保证农村经济不断增长和农村生态系统良性循环的一个非常重要问题。农业生态系统边界范围较大,具有多层次、多因素、多目标、多途径等复杂性,要想深刻剖析农业生态系统结构和功能的关系,必须用系统工程的观点和方法对农业生态系统的结构进行控制和管理。本文通过对建平县农业     

Computed three-dimensional structures for theras-binding domain of theraf-p74 protein complexed withras-p21 and with its suppressor protein, rap-1A

The three-dimensional structures of theras-p21 protein and its protein inhibitor, rap-1A, have been computed bound to theras-binding domain, RBD (residues 55–131), of theraf-p74 protein, a critical target protein ofras-p21 in theras-induced mitogenic signal transduction pathway. The coordinates of RBD have been reconstructed from the stereoview of an X-ray crystal structure of this domain bound to rap-1A and have been subjected to energy minimization. The energy-minimized structures of bothras- p21 and rap-1A, obtained in previous studies, have been docked against RBD, using the stereo figure of the RBD-rap-1A complex, based on a six-step procedure. The final energy-minimized structure of rap-1A-RBD is identical to the X-ray crystal structure. Comparison of theras-p21- and rap-1A-RBD complexes reveals differences in the structures of effector domains ofras-p21 and rap-1a, including residues 32–47, a domain that directly interacts with RBD, 60–66, 96–110, involved in the interaction ofras-p21 withjun kinase (JNK) andjun protein, and 115–126, involved in the interaction of p21 with JNK. The structure of the RBD remained the same in both complexes with the exception of small deviations in its-2 binding loop (residues 63–71) and residues 89–91, also involved in binding to rap-1A. The results suggest that the binding of these two proteins to RBD may allow them to interact with other cellular target proteins such as JNK andjun.     

Algae on the internet

Increasingly electronic communication and a variety of electronic resources are accessible to a larger group of people within the scientific community. This paper outlines the range of resources that are available, and comments on their current and future value to the phycological community. Resources discussed include mailing lists and newsgroups. These are useful tools for rapid, informal, targeted communication, although the technology employed places limitations on the type and format of information which may be distributed. The World Wide Web (WWW) has the potential to overcome these limitations, the quality, complexity and value to the phycological community of the sites on the WWW are extremely variable, with some material being of dubious quality. However, it is possible to access high quality resources including culture collection catalogues, high quality images and microbial and molecular databases. As well as some of the current resources, this paper discusses some possible directions for the future of phycology on the internet.http://wiua.nwi.ac.uk/     

Thermodynamics of staphylococcal nuclease denaturation. II. The A-state.

Staphylococcal nuclease, at low pH and in the presence of high salt concentrations, has previously been proposed to exist in a partially folded or molten globule form called the "A-state" (Fink et al., 1993, Protein Sci 2:1155-1160). We have found that the A-state of nuclease at pH 2.1 in the presence of moderate to high salt concentrations and at low temperature exists in a substantially folded form structurally more similar to a native state. The A-state has the far-UV circular dichroism spectra characteristic of the native protein, which indicates that it has a large degree of secondary structure. Upon heating, the A-state denatures with a sigmoidal change in far-UV ellipticity and an observable peak in a differential scanning calorimeter trace, indicating that it is thermodynamically distinct from the denatured state. Three different mutations in a residue normally buried in the protein's core stabilize or destabilize the A-state in the same way as they affect the denaturation of the native state. The A-state must, therefore, contain at least some tertiary packing of side chains. Unlike the native state, which shows cold denaturation at low temperatures, the A-state is most stable at temperatures below 0 degrees C.     

滇蜀豹子花核型及其变异研究

本文详细报道了滇蜀豹子花的核型,发现居群中存在两种细胞型,即A型和B型。A型参考核型为2n = 24＝2m(2SAT)+2sm+8st(4SAT)+12t(2SAT),其第3号两条同源染色体长臂均无居间随体：B型参考核型为2n=24＝2m(2SAT)+2sm+8st(2SAT)+12t(3SAT)+0—1b,其第3号一条同源染色体长臂紧靠着丝点处有一大而明显的居间随体,而另一条同源染色体则无,构成明显的3号染色体的结构杂合性。统计表明,居群中二者的比例近似为1A;2B。研究还发现了大量的体细胞染色体结构变异核型,表明滇蜀豹子花核型尚未趋于稳定,还处于强烈分化之中,高频率的体细胞染色体结构变异是其种内分化不可忽视的一种进化要素。     

Conservation,protected areas and the global economic system: how debt,trade, exchange rates,inflation and macroeconomic policy affect biological diversity

The main characteristics of the dominant economic system, including the increasing use of markets and money are described. The global system has expanded trade, including international trade, and production tremendously. While this system has the potential to favour nature conservation, in practice the opposite has occurred. Difficulties raised for conservation of biodiversity by short-term economic crises such as deficits in a country's international payments, the adoption of policies for structural economic adjustment, international capital flows, international loans and foreign aid as well as debt-for-nature swaps are discussed. As explained, it is politically difficult in market economies to support nature conservation at the expense of economic growth and as more economies develop and become market economies this problem spreads. Given global interdependence of nations, an important issue is the distribution of net benefits from biodiversity conservation between developed and less developed countries. Possible distributions of benefits and related issues are discussed. In conclusion, the importance of political lobbying by nature conservation groups in developed market economies is emphasised as a means of ensuring correction of market failures. Unfortunately, no economic system is likely to prove satisfactory in itself in conserving biodiversity so political action by conservationists is always required.     

Human-modified landscapes driving the global primate extinction crisis

The world's primates have been severely impacted in diverse and profound ways by anthropogenic pressures. Here, we evaluate the impact of various infrastructures and human-modified landscapes on spatial patterns of primate species richness, at both global and regional scales. We overlaid the International Union for the Conservation of Nature (IUCN) range maps of 520 primate species and applied a global 100 km² grid. We used structural equation modeling and simultaneous autoregressive models to evaluate direct and indirect effects of six human-altered landscapes variables (i.e., human footprint [HFP], croplands [CROP], road density [ROAD], pasture lands [PAST], protected areas [PAs], and Indigenous Peoples' lands [IPLs]) on global primate species richness, threatened and non-threatened species, as well as on species with decreasing and non-decreasing populations. Two-thirds of all primate species are classified as threatened (i.e., Critically Endangered, Endangered, and Vulnerable), with ~86% experiencing population declines, and ~84% impacted by domestic or international trade. We found that the expansion of PAST, HFP, CROP, and road infrastructure had the most direct negative effects on primate richness. In contrast, forested habitat within IPLs and PAs was positively associated in safeguarding primate species diversity globally, with an even stronger effect at the regional level. Our results show that IPLs and PAs play a critical role in primate species conservation, helping to prevent their extinction; in contrast, HFP growth and expansion has a dramatically negative effect on primate species worldwide. Our findings support predictions that the continued negative impact of anthropogenic pressures on natural habitats may lead to a significant decline in global primate species richness, and likely, species extirpations. We advocate for stronger national and international policy frameworks promoting alternative/sustainable livelihoods and reducing persistent anthropogenic pressures to help mitigate the extinction risk of the world's primate species.     

Causal inference and large-scale expert validation shed light on the drivers of SDM accuracy and variance

Aim

To develop a causal understanding of the drivers of Species distribution model (SDM) performance.

Location

United Kingdom (UK).

Methods

We measured the accuracy and variance of SDMs fitted for 518 species of invertebrate and plant in the UK. Our measure of variance reflects variation among replicate model fits, and taxon experts assessed model accuracy. Using directed acyclic graphs, we developed a causal model depicting plausible effects of explanatory variables (e.g. species' prevalence, sample size) on SDM accuracy and variance and quantified those effects using a multilevel piecewise path model.

Results

According to our model, sample size and niche completeness (proportion of a species' niche covered by sampling) directly affect SDM accuracy and variance. Prevalence and range completeness have indirect effects mediated by sample size. Challenging conventional wisdom, we found that the effect of prevalence on SDM accuracy is positive. This reflects the facts that sample size has a positive effect on accuracy and larger sample sizes are possible for widespread species. It is possible, however, that the omission of an unobserved confounder biased this effect. Previous studies, which reported negative correlations between prevalence and SDM accuracy, conditioned on sample size.

Main conclusions

Our model explicates the causal basis of previously reported correlations between SDM performance and species/data characteristics. It also suggests that niche completeness has similarly large effects on SDM accuracy and variance as sample size. Analysts should consider niche completeness, or proxies thereof, in addition to sample size when deciding whether modelling is worthwhile.     

Three-dimensional species distribution modelling reveals the realized spatial niche for coral recruitment on contemporary Caribbean reefs

The three-dimensional structure of habitats is a critical component of species' niches driving coexistence in species-rich ecosystems. However, its influence on structuring and partitioning recruitment niches has not been widely addressed. We developed a new method to combine species distribution modelling and structure from motion, and characterized three-dimensional recruitment niches of two ecosystem engineers on Caribbean coral reefs, scleractinian corals and gorgonians. Fine-scale roughness was the most important predictor of suitable habitat for both taxa, and their niches largely overlapped, primarily due to scleractinians' broader niche breadth. Crevices and holes at mm scales on calcareous rock with low coral cover were more suitable for octocorals than for scleractinian recruits, suggesting that the decline in scleractinian corals is facilitating the recruitment of octocorals on contemporary Caribbean reefs. However, the relative abundances of the taxa were independent of the amount of suitable habitat on the reef, emphasizing that niche processes alone do not predict recruitment rates.